CdTe and CdMTe (M = Fe, In, Sb) thin film studies by Mössbauer spectroscopy and other techniques

Non-destructive characterization of the atomic and electronic structures hasbeen carried out for CdTe and CdMTe (M = Fe, In or Sb) thin films. These films were grown either by sputtering or by close-spaced vapour transport techniques. Characterization was performed using the time-of-flight technique and four spectroscopies: Mössbauer, X-ray diffraction, Auger electron and photoluminescence. Different kinds of compound materials can be obtained when CdTe and indium (or antimony) are co-sputtered. A monotonic increase in indium concentration leads to the successive formation of Cd_0.83In_0.34Te_1.34, CdIn₂Te₄ and InTe; we demonstrate the role of indium substituting for cadmium. A monotonic increase in antimony in CdSbTe films leads to amorphization of its atomic structure; it is probable that antimony has an amphoteric behaviour, with nearly equal chances of substituting for either cadmium or tellurium in the CdTe lattice. The ionicity of iron was used in order to determine the amorphous: crystalline ratio in CdFeTe films. Finally, low temperature photoluminescence, measured in CdTe polycrystalline films, is compared with electron and hole lateral mobilities measured on the same films. This comparison shows that the intracrystalline and/or intercrystalline density of defects is larger in large grain films than in small grain films. In any case, charge carrier (both electrons and holes) transport in the films is a trap-controlled process.